Finned cylinder for internal-combustion engines and method of making same



Dec. 20, 1949 s. SPAGNOLA 2,491,878

FINNED CYLINDER FOR INTERNAL COMBUSTION ENGINES AND METHOD OF MAKING SAME Flled March 15, 1947 5 WW M T N N MR E6 0 VL n E A W 6 fl saw 5 5 E M 2 N li s-floated Eco. 20, fi w FINNED CYLINDER FOR- INTERNAL-COM BUSTION ENGINES MAKING SAME AND METHOD OF Samuel Spagnola, Bronxville, N. Y.

Application March 15, 1943. Serial No. 2134.979

12 Claims. 3

This invention relates to air cooled internal combustion engine cylinders, heat exchangers and the like and the manufacture thereof.

A conventional method in the manufacture of cylinders for air cooled internal combustion engines is first to make iorgings of the desired diameter and wall thickness which include the depth of the fins. These i'orgings are usually made of a nitrc-alloy which possesses, the unusual property oi becoming glass hard when heated to a temperature of 1000 F. in the presence of ammonia gas. Since this degree of hardness is required only 'in the bore to resist wear,

' the cylinder forms after rough machining the 'outside and semi-machining the inside, are tin 'plated all over by an automatic machine which also washes and dries them, usually at the rate of about thirty-two an hour. The tin plate is then removed from the bore and the bore ground within about .001 inch of the desired bore. The cylinder forms are now ready for the hardening method of hardeningthe bores of the cylinder of the bore by the nitriting process which consists of 7 loading the cylinder forms into large porcelain-lined or enamel-lined containers covered with large bell-shaped"covers whose lower edges rest in a trough filled with chromium ore to prevent escape of gas. After this treatment the containers are uncovered and after cooling to room temperature the treated cylinder forms are removed from the containers. The complete cycle usually requires forty-five hours, of which ten hours are required to bring the cylinder forms up to the desired temperature and thirty-five hours to secure the desired depth of case hardening of about 0.022 inch. After the nitriting process the outsides of the cylinder forms which have been protected by the tin plate coating and therefore not hardened, at least not hardened to the extent the bore is hardened, are finished and machined. The cooling fins are formed by means of an expensive automatic machine with a magazine tool holder to permit the cutting of all the fins at one time in the cylinder. This operation is followed by the formation of the required threading at the head end of the cyLnder preparatory to the assembly of the cylinder head. A completed cylinder weighing twelve pounds is sometimes formed from a rough forging weighing as much as sixty-two pounds, indicating the large quantity of material required to be removed, and the conventional process above described also otherwise involves considerable time and expense in the manufacture.

One object of the inventionis a novel and improved method of manufacturing air cooled engine cylinders and other heat exchangers.

A further object of the invention is a method of manufacture which is characterized by its simplicity, its low cost, a better resulting unit and fewer rejects.

units.

A further object of the invention is a novel method of attaching flanges and the like on. cyl inder forms or units.

Further objects of the invention will hereinafter app ar.

. For a better understanding of the invention reference may be had to the accompanying drawings forming a part of this application, wherein Fig. 1 is a diagrammatic side view of a means for facilitating the practice oitheinvention;

Fig. 2 is a view along the line 2-2 of Fig. 1;

Fig. 3 is a diagrammatic view illustrating another feature of the invention;

Fig. 4 is a view diagrammatically illustrating certain steps in. the method of practicing the invention; and

Fig. 5 is a diagrammatic view showing an alternate embodiment of the invention.

In Figs. 1 to 3 I have illustrated my invention as applied to the manufacture of air cooled cylinders for internal combustion engines. Instead of forming a cylinder form forging as is done according to the above described conventional practice, I start with the formation of 9. rolled steel cylinder of predetermined external and internal dimensions which requires no external milling or cutting. The cooling fins or flanges are formed about the cylinder by winding 8. metallic wire or ribbon about the cylinder in a continuousmanner and in superposed layers continuously welded to each other as the winding progresses until the predetermined depth of fin or flange is obtained. This may be effected by winding the wire or ribbon spirally about the cylinder to form a continuous spirally wound flange or fin or it may be eflected by forming separate flanges or fins spaced from each other longitudinally of the cylinder the desired dis- The heating of the metallic wiretance apart. or ribbon to the welding temperature may be effected in any suitable manner, as by blow pipe, double carbon electrode or Zerener method, gas are or atomic hydrogen method, the single carbon electrode Bernardose method, the metallic electrode or Slavianoif method or any suitable electrical or electronic method. 7

In Figs. 1, 2 and 3 I have illustrated my invention as applied to the making of air cooled internal combustion engine cylinders. A cylinder I is first formed of the required internal and external dimensions with no cooling fins or flanges thereon. This cylinder may be of any suitable metal as, for example, conventional rolled steel. It is mounted on an apparatus for relative rotation with respect to the wire or ribbon supply means for forming the fins or flanges thereon. In the particular embodiment this cylinder l is 4 contactwith the cylinder or fin and the fin is gradually built up. Welding current is supplied the motor 8 is geared down to the shaft I to drive I the latter at the speed desired through any con ventional drive means such, for example, as that indicated diagrammatically at 9. The flanges or fins III are formed upon the cylinder I by the continuous feeding of a wire strip or ribbon II of the metal which is to form the fins or cooling flanges I0. This ribbon II is fed from a reel or other supply (omitted for convenience in illustration) and is fed in the direction of the arrow illustrated in Fig. 2. It is fed in the plane of the fin or flange to be built up. It is fed approximately tangentially to the cylinder I or to the surface of the tin being built up and heat is applied to the wire II and to the surface underneath as indicated by the arrow I2. This heat is continuously applied and in sufficient quantity to cause the wire or ribbon II to be welded in superposed layers to itself as it is fed onto and wound about the cylinder. In the particular embodiment shown the heat is applied by an electric current through the medium of a copper roller I3 which conducts a welding current to the ferrous or non-ferrous wire or ribbon II and to the under surface to which it is to be welded. This roller electrode I3 is carried by a frame member I4 and the roller electrode is mounted on a bearing I5 mounted on the elongated frame member l4, the latter extending above and crosswise of the cylinder I. This frame member II is pivotally attached at I6 to the upper end of an upstanding frame member I! and by reason of this mounting the frame member I4, being free at its other end, causes the roller electrode I3 to rest by gravity upon the fin being built up and at the point where the wire or ribbon I I engages the fin. The frame member I4 at its free end is provided with a downwardly extending bracket la in which is iournaled a guide roller I9 which is mounted in the plane of the fin being built up and guides the wire H on its way to the fin being built up. The free end of the frame member I4 also has journaled therein an auxiliary roller electrode which is journaled in a suitable bearing 2| mounted on the free end of the frame member I4. The bracket l8, the rollers I8 and 20 and the weight of the frame member I4 function to maintain the roller electrode l3 in firm contact with the wire II and the fin. This gravitational action of the several members supporting the roller I3 may be supplemented by a suitable expansion spring 22 acting between the stop 23 and the frame member l4 to increase the pressure of roller I 3 on the wire II and the fin. It is understood that the roller electrode I3 is insulated from the frame member I4 and similarly the auxiliary roller electrode 20 is insulated from the frame member I4. With the cylinder I rotating in the direction of the arrow (Fig. 2) and the wire or ribbon II fed in the direction of the arrow, the welding current is supplied through the contacting point I2 with the result that the wire or ribbon is continuously welded to the surface of the fin as the former comes tangentially into to the welding roller 43 through leads 25 and 26. the lead 28 leading to the roller 43 and the lead 25 leading to a brush 2! (Fig. l) in engagement with the periphery .of the chuck 2. These leads 25 and 26 are supplied with welding current from the secondary of a transformer 28. The conductor "is connected with a brush 30 which is in contact with the periphery of the welding roller l3, this brush 30 being carried by a frame member 1" insulatedly supported by the frame .support'member I4. The roller I3 is provided with a shaft member 32 which is journaled in the sleeve bearing Ilwith an insulating sleeve 33 the'rebetween. In like manner the rollers I9 andv 20 are insulatedly journaled respectively on the .frame member I4 and the downward extension I8 thereof. The brush 2'! is carried or guided by a suitable i; ame 21-.

The upstanding frame member I! is carried by a carriage 35, the latter being adapted to follow suitable guides 36 and 31 supported in any suitable manner as, for example, by the upstanding frame member 4 at one end and an upstanding frame member 5 disposed at one end of the base 5. The member 35 functions only as a guide while the guide member 36 also is in the form of a screw shaft screw threadedly attached to the carriage 35. By rotating the screw 35 which is journaled in the frame members 4 and 5' the frame support I I, I4, I8 may be advanced longitudinally of the cylinder I to provide for the advance of the welding roller l3 from one finished fin III to a position to build up the next succeeding fin on the cylinder. The shaft 36 may be rotated in any suitable manner as, for example, by means of a handle 38 carried by a calibrated index dial 39 fastened to the end of the screw shaft 36. This calibrated index dial enables the operator to set the welding roller I3 for the desired pitch of the fins prior to the beginning of the building up operation.

The wire or ribbon II may if desired be preheated by the passage of heating current therethrough just prior to its reaching the welding roller I3. This may be accomplished by an auxiliary circuit including an adjustable rheostat 43, switch 42 and wire 40 to the brush 4| bearing upon the periphery of the roller 20. With the switch 42 closed, a portion of the current is directed from the secondary of the transformer 23 to the roller 20, through the wire II to the frame and thence by the brush 2! and lead 25 to the opposite side of the secondary winding, the rheostat 43 being adjustable to effect the desired degree of preheating for the wire II during the performance of the actual welding operation at I2.

I have illustrated diagrammatically a power supply circuit for the transformer 28 comprising a main line switch 45 for connecting the main supply source 46 with the supply line 41 leading to a conventional electronic control unit diagrammatically illustrated at 48. This unit comprises the conventional rectifier units for supplying direct current to the motor 8. The circuit is so connected that the speed of the motor 8 is caused to increase or decrease to facilitate the proper welding of the wire during the building up of the fin, as for example, the arrangement being such as to increase the speed of the motor with increase of welding current load. The details of the control are omitted from the drawings for convenience in illustration since the control per se is conventional in other welding processes and forms no part of the present invention.

The direct current is supplied through lines 50 leading to the motor 8. The motor is provided with a terminal block 51 to which the line conductors II lead. The primary of the transformer 2. is supplied with current from the lines 11 through the unit 48 by the lines 52 and 53. A two wire control line 55 leads from the unit 45 to a manual control 56 which is diagrammatically illustrated as of the push button type for starting and stopping the operation. A quick break control switch 51 pivoted at 58 to a suitable part of the frame structure is disposed in the line 53 so as to open 'and close that line at the contact I. This switch functions as a limiting switch and relay for interrupting the supply of primary current to the transformer 28 when a cooling fin or flange of the desired depth is reached. This control is efiected by mounting upon the frame member II a switch interrupting member 60 having a lug 6| which engages the switch 51 on the opposite side of the pivot 58 from the contact 59 to break the circuit 53 when the fin l being built up is of the desired height. The frame member ll gradually pivots in a clockwise direction about the pivot It as the fin is built up and accordingly gradually elevates the switch interrupter 60 to effect this control. The operation is as follows. A steel cylinder I, preferably of rolled steel, is attached to'the chuck 2 in line with the axis of rotation of the chuck 2 as, for example, by being screw threadedly attached as indicated at 3. The carriage 35 is then adjusted to bring the roller electrode l3 to the position to begin the building up of the first fin or flange to be made. The frame member I4 is lifted in a clockwise direction about its pivot l6 to permit the end of the wire or ribbon H to be inserted under the roller electrode l3 ior starting the formation of the fin. The circuit is closed at switch 45 and through start stop switch 55 to supply A. C. current to the unit 48 and the transformer 28 and welding current is thereby passed through the rollerelectrode l3 into the cylinder I and the end of the wire or ribbon H is thereby welded to the cylinder. This welding takes place simultaneously with the energization of the driving motor 8 which then starts the rotation of the cylinder in a direction to build up the fin. If desired there may be a time delay between the supply of current to the welding electrode l3 and the starting of the motor so as to assure a weld sufficient to pull the wire or ribbon ii at the starting of the motor, although little or no tension is required to be exerted on the wire or ribbon ii to reel it from the supply reel and the weight of the frame member I4 and the rollers i3, i9 and 2|) assists in holding the wire or ribhon H on the cylinder at the starting. If the pressure exerted by the roller electrode I3 is insuflicient, spring pressure by means of an expansion spring 22 may be added to the weight of the frame member [4 and the rollers carried by it to apply the desired pressure at the welding point or contact of the roller electrode l3. After the desired depth of a fin I0 is reached, the limit switch 51 is operated by the interrupting member to open. the primary circuit of the transformer 28. The index wheel 39 is turned through the required degree to move the carriage 35 together with the roller electrode l3 through the desired fin pitch, whereupon the operations are repeated in building up the next fin. Any depth of fin and pitch desired may be provided. In some instances the fin has a depth of around 0.7

inch and the pitch or distance between the adjacent fins at any point is about 0.25 inch in some cases.

In'the particular embodiment described above, the fins or flanges ID are formed into separate parts disposed at planes at right angles to the axis of the cylinder instead of having a continuous spirally wound and built up fin for the whole cylinder. For building up a single continuous spirally wound fin the screw 36 may be driven synchronously with the cylinder with provision for either shifting the roller electrode I: back to one end of the cylinder after it has reached the other end to build up another layer on the fln or providing a duplicate set of welding rollers and supports on the opposite side of the cylinder to permit reversing of the drive 36 and the application of the second or alternate layers by such duplicate equipment.

My invention thus obviates the necessity of using expensive special equipment and results in considerable saving of time and cost generally in the manufacture of these air cooled internal combustion engine cylinders as compared with the conventional method described above. Moreover, since the rolled steel cylinders are more homogeneous in fiber structure thanthe conventional forged steel forms, considerably fewer flaws and less rejects are present with my invention and a stronger cylinder unit is thereby provided. Also since I start out with merely a rolled steel cylinder of predetermined outer dimensions with no surplus material needing to be removed in the formation of the fins, there is required considerably less time to bring the charge to the proper heat with a considerable saving in that respect. The hardening of the interior surface of the cylinder requires often as much as thirtyfive hours in the conventional practice and another feature of my invention resides in the .utilization of high frequency current for heating the interior of the bore with the frequency and heat being of the desired values for the case hardening depth and the unit quenched whereby this can be eflfected in considerably less than the time required in conventional practice. Moreover by using high frequency heating for the hardening of the inner surface of the cylinder the cylinder may be processed either before or after the provision of the fins. This same high frequency current may also be used in the welding process in the building of the fins. If the cylinder bore is hardened before the fins are wound, the interior of the cylinder would be cooled so as not to draw the temper.

As indicated above, certain features of the invention are applicable to the building up of the fins and flanges on other forms of heat exchangers than air cooled combustlon engine cylinders as, for example, superheaters, refrigerator units, etc. In Fig. 3 I have diagrammatically illustrated the invention as applicable to cylinders or other heat exchangers of suitable structure and character wherein in Fig. 4A I have illustrated a unit Hi which is to be converted into a heat exchanger device. In Fig. 413 I have illustrated the fins III as having been built up on the unit 10 in accordance with my invention and at H I have illustrated a fln being built up and before it is finished. In P18. 40 I have indicated the strip or ribbon of metallic wire ll being fed to the unit 10 and building up the fin H. The arrow 12 indicates the point of application of the welding heat and pressure if desired. As above described, this heat may be applied by high frequency currents, by direct application of welding current as illustrated in Figs. 1 and 2 by the use of a blow pipe, by the use of a double carton electrode or Zerener method, by the use of a gas are or atomic hydrogen are or by the single carbon electrode Bernardos method, or by the metallic electrode or Slavianoif method.

In Fig. 1 I have shown the cylinder I provided with a flange 15 for bolting or attaching the cylinder to an engine crank case and as applied to other heat exchangers. This flange I5 may be used for attaching to another pipe flange in the heat exchanger. In Fig. 3 I have illustrated certain features of my invention as applied to the formation of such attaching flanges. Referring to this figure the heat exchanger form is indicated at I5 and at 11 I have illustrated the formation of the attaching flange about the unit I5 by winding the wire or ribbon about the unit 15 in adjacent planes and of difierent depths. In this case the wire, which is squared, is wound in layers closely adjacent to each other as indicated by the numerals I, 2, 3, 4, 5 and 6 which form one layer. The next superposed layers are positioned upon the first layers I, 2, 3, 4, 5 and G and so on until the end layer is built up of a depth greater than all the other layers, and in the particular embodiment shown two layers higher while the other layers are of depths varying successively in height by one layer. These different layers of. welded wire may be effected in any suitable order as, for example, by winding and welding the first layers I to 5, inclusive, next the layers I, 8, 9, I and II, next the layers I2, I3, I4 and I5, next the layers I6, II and I8, next the layers I9 and 20 and then in succession the layers M and 22 upon each other. In this structure each of the superposed layers is welded to the next layer so that a welded mass is obtained of the general shape shown in Fig. 4 which may then be machined along the line I8 to machine and smooth oil the sharp corners. This flange 11 thus formed may be bored for the reception of attaching bolts and the like. If desired the fins III of Fig. 1 may be formed instead of one thickness of wire layers superposed upon each other, of two or more adjacent layers which are closely disposed and welded sidewise to each other, although for cooling tins and flanges the preferred structure is the utilization of a wire or ribbon II of sufficient width to build up a fin by one winding or layers of windings in superposed position to give the desired thickness of the fins.

In Fig. I have illustrated in fragmentary form. an alternate embodiment of the invention which diflers from that shown in Fig. 1 by the inclusion of means for simultaneously welding to a cylinder, such as the cylinder I of Fig. 1, two or more fins in the manner heretofore described. In this figure, I denotes the cylinder to which two or more fins III are to be welded and which is threadably attached to the chuck 2. The weldin operation is accomplished by means of a cylindrical roller I3 of sufficient length to span that portion of the cylinder I on which the fins are to be welded. This roller I3 is rotatably supported at its ends by frame members I4 and I4 in substantially the same. manner as the roller I3 in Fig. 1 was supported by its frame member I4. These frame members are in turn pivotally carried by upwardly extending brackets I1 and II, respectively, which are fixed to or movable in unison on the bed or frame of the machine. Guide rollers, similar to rollers II and 20 of Fig. 2, for feeding the ribbon or wire to form the fin may be provided and suitably mounted for each of the fins to be welded or a pair of cylindrical rollers similar to the roller I3 may be used to feed all the wires simultaneously. In the latter case, th horizontal frame members I4 and I4 would carry on their free ends the upper cylindrical guide roller or rollers, preferably a roller for each strip similar to the roller 20 of Figs. 1 and 2 and performing the same function. Also the frame members I4 and I4 carry suitable supports for supporting guide rollers like the roller I9, preferably a separate roller for each strip as, for example, by suitable support members like I8 dependent downwardly and supported from the free ends of the members I4 and I4.

The electric current for the Welding operation may be supplied by a suitable transformer, such as transformer 28 in Fig. 2 through leads 28 and 25. The lead 26' is connected to the roller I3 by a brush 30 insulatingly supported by a frame member 3I'. The return circuit may be accomplished by means of a second brush Z'I contacting and slidable on the chuck 2 and connected with the lead 25' in substantially the same manner heretofore described in connection with that embodiment of the invention shown in Fig. 1. Similarly a preheating circuit including a rheostat may be associated with the guide rollers to preheat the wire prior to the actual welding operation. In that instance the guide rollers must be insulated from the frame members I4 and I4 so that the heating current will pass through the wire and accomplish the desired degree of heating.

Extending upwardly of the frame member I4 is a member having a lug 6| for engagement with and operation of the limit switch 58. This limit switch, similar to that described in Figs. 1 and 2, operates to open the welding transformer circuit when the fins have attained a desired height and stops the welding operation.

This last embodiment of the invention manifestly provides not only the advantages set forth in' the form shown in Figs. 1 and 2, but also a further reduction in the time required for the welding operation. This procedur insures a substantially uniform fin formation, and errors in spacin the fins one from the other would be more easily detected prior to the welding operation.

It is understood that the claims hereto attached are not to be construed as limited to the particular means shown and described except as the language of the claims may require such limitation. For example, the control switch mechanism 51, 58 and 60 is merely one means which may be employed for closing the circuit or keeping the circuit closed until the fin or fins are built up to the desired height and then the circuit to transformer interrupted, as for example, a conventional photocell mechanism or other electronic devices may be employed. Other and suitable means may be Provided for transmitting the welding current to the welding point or for heating the strip or wire at the point of weld and while I have shown this strip or wire II somewhat diagrammatically, it is understood that this may be either solid or hollow and by making the strip hollow and welding the strip about the cylinder to form the fin without heating the hollow strip or tube sufficiently and without applying pressure sufliciently to close up the hollow strip or tube at any point, cooling fluid may be passed through this hollow tube or wire forming the fin with marked improvement in cooling efficiency.

I claim:

1. The method of forming a cooling fin on a metallic heat exchange device comprising the steps of feeding a metallic strip of a metal of which the fin is to be formed to the device and while imparting relative rotation between the device and the strip, welding the strip in superposed single radially coplanar turns thereon to build up the fin to the desired depth.

2. The method of forming a cooling fin on a metallic internal combustion engine cylinder comprising the steps of winding a strip of metal about the cylinder in superposed radial turns and progressively welding the superposed turns together as the strip is wound about the cylinder.

3. The method of making a hollow heat exchange device comprising the steps of makinga hollow metallic form and then building up on said form a cooling fin by winding a strip of metal about the form in superposed radial turns and welding the superposed turns together.

4. The method of making a heat exchange device comprising the steps of making a cylindrical metallic form and then forming a multiplicity of cooling fins thereon by winding metallic strips about the cylindrical form in overlying radial turns and progressively welding the strips to the cylinder and each turn to the next preceding turn to form spaced cooling fins thereon.

5. The method of forming cooling fins on a metallic cylinder comprising the steps of feeding a metallic strip to and winding the same about the cylinder in superposed radial turns and electrically welding the strip to the cylinder and the successive turns of strip by maintaining the strip under the desired pressure as it engages the cylinder and passing an electric current through the point of engagement of the strip with the cylinder.

6. The method of forming cooling fins on a metallic cylinder comprising the steps of feeding a metallic strip to and winding the same about the cylinder in superposed radial turns, and electrically welding the strip to the cylinder and each successive turn to the next preceding turn of strip by maintaining the strip under the desired pressure as it engages the cylinder and the fin being built up, and passing a current through the point of engagement, and including the step of applying heating current tothe strip prior to its reaching the welding electrode.

7. The method of forming two or more coolin fins on a metallic heat exchange device comprising the steps of feeding two or more metallic strips of which the fins are to be composed, and

geneous annular cooling fin, the thickness of said fin being determined by the width of the strip and similarly forming successive spaced fins in like manner on said cylinder.

9. A metallic cylinder for internal combustion engines, comprising a plurality of metallic annular cooling fins in spaced relationship one to the while imparting relative rotation between the de-.

vice and the strip simultaneously and continuously welding the strips in individual superposed radial turns to simultaneously build up the two or more fins to the desired depth.

8. The method of forming spaced cooling fins on a metallic internal combustion engine cylinder, comprising feeding a metallic strip to the cylinder while imparting relative rotation between the cylinder and the strip to form a helically wound fin with successive turns of said strip superposed radially one upon the other to build up the fin to the desired depth, and progressively welding the first turn of the strip to the cylinder and each successive turn to the next preceding turn of said strip to form a substantially homoother on the outer surface of said cylinder, each of said fins being formed of a multiplicity of su-' perposed coplanar helical turns of'.metal strip with the inner turn welded to the cylinder and the superposed turns welded to each other, with the thickness of each fin being determined by the width of the strip. I

10. The method of forming spaced cooling fins on a metallic internal combustion engine cylinder comprising the steps of feeding metallic strips to the cylinder in planes spaced longitudinally of the cylinder length while imparting relative rotation between the cylinder and the strips to form helically wound fins with the successive turns of each of the strips superposed radially one upon the other to build up the fins to the desired depth and progressively welding the first turn of each strip to the cylinder and the successive turns thereof to the next preceding turns respectively to form substantially homogeneous annular cooling fins, the thickness of the fins being determined by the widths of the strips.

11. The method of forming spaced cooling fins on a metallic internal combustion engine cylinder, comprising feeding a metallic strip to the cylinder while imparting relative rotation between the cylinder and the strip to form a helically wound fin with successive turns of said strip superposed radially one upon the other to build up the fin to the desired depth, and progressively electrically welding the first turn of the strip to the cylinder and each successive turn to the next preceding turn of said strip to form a substantially homogeneous annular cooling fin, the thickness of said fin being determined by the width of the strip and similarly forming successive spaced fins in like manner On said cylinder.

12. A-cylinder for'internal combustion engines comprising a steel cylinder of predetermined external and internal dimensions and a cooling fin structure applied to the outer surface of said cylinder and formed of a plurality of superposed radial turns of metallic strip material built up to form a structure of the desired radial fin height with the innermost strip material welded to the cylinder and successive turns welded to the next preceding turns, the thickness of said fin structure being determined by the width of the strip material.

SAMUEL SPAGNOLA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,323,621 Edwards Dec. 2, 1919 1,909,704 Morseth May 16, 1933 2,349,496 Gillum et al May 23, 1944 2,433,966 VanKeuren Jan. 6, 1948 FOREIGN PATENTS Number Country Date 397,944 France Mar. 11, 1909 399,959 France July 13, 1909 

